Many oxygen sensitive products, including food products such as meat and cheese, and smoked and processed luncheon meats, deteriorate in the presence of oxygen. Both the color and the flavor of foods can be adversely affected. The oxidation of lipids within the food product can result in the development of rancidity. These products benefit from the use of oxygen scavengers in their packaging.
Certain food products such as poultry and process poultry meats (e.g., sausage, ham salami, and pepperoni, e.g. turkey pepperoni) can generate sulfur off odors. The origin of these odors is most likely enzymatic or microbial degradation of sulfur containing amino acids. This is particularly a problem in high oxygen barrier packaging. Hydrogen sulfide and other sulfur containing compounds, such as mercaptans are generated during the normal shelf life of these products particularly at room temperature and to a lesser degree under refrigerated storage.
Poultry often forms sulfur-containing components during storage. Although the poultry may still be safe for consumption, the odors cause consumers to regard it as “spoiled” and return the poultry to the retailer. As a result, poultry cannot be packaged in barrier films due to the necessity for releasing the generated sulfur type off-odors. These factors limit the shelf-life of the fresh product to typically fourteen days after processing for chicken parts.
Iron based oxygen scavenging sachets have been found to be good scavengers of sulfur odors. Unfortunately, iron based oxygen scavenging sachets have their own drawbacks when used in food packaging. These drawbacks include incompatibility with metal detectors, as well as the potential for accidental ingestion of the sachet contents.
Organic, inorganic and polymeric oxygen scavengers are known, these materials typically incorporated into the packaging material itself. However, it has now been found that sulfur off-odors are sometimes exacerbated in packages containing oxygen scavengers. Thus, to replace iron-based sachets, for example with oxygen scavenger containing films, an alternative means of removing sulfur odors is needed.
An additional challenge for many packaging applications is the requirement that the packaging material, such as a film, be transparent or nearly transparent. Many functionally useful materials, either for hydrogen sulfide scavenging or oxygen scavenging, cause a film into which they are incorporated to become opaque, or at least degrade the optics of the film to an extent to make them unfit for packaging applications where the film customer or final user desires a clear film in which the contents of the package can be visually inspected from outside the package.
It has now be found that various additives can be incorporated into articles such as polymeric films, sachets, purge control pads, or labels, and scavenge sulfur odors with in many cases no or minimal impact on optical properties of the film. Materials of the present invention can adsorb hydrogen sulfide and methyl mercaptan as they are formed, and thus offer extended shelf-life of the packaged product, and/or the ability to implement an oxygen scavenger in conjunction with a sulfur scavenger.
These additives include ultra fine copper powder (with a mean particle diameter of 0.2 micrometers), more generally copper (0) powder, copper (0) on a high surface area support, copper (II) on a high surface area support, and zinc acetate. These sulfur scavengers were found to be most effective when moist. In addition, we have found that zinc oxide has also proved effective, and has an advantage of being categorized as “GRAS” (Generally Regarded as Safe) by the US Food and Drug Administration.
Other materials have also been found to be useful as sulfur scavengers include zinc stearate (also “GRAS”), copper (II) oxide, iron oxide powder and zinc ionomer (e.g., SURLYN™ available from DuPont). Nano particle sized zinc oxide can be used at relatively high loadings while maintaining good optical properties. On the other hand, while ultra fine (i.e. having a mean particle diameter of less than 0.2 micrometers) copper (0) powder is very effective, somewhat larger particle size materials (1 to 3 micrometers) are actually less colored in the polymer matrix. Larger particle copper powder is also less expensive. “Copper (0)” herein means copper in its zero valence state.
GC headspace tests were run to determine the effectiveness of various materials either in their pure state or as compounded into low density polyethylene and/or zinc ionomer. Contact ratios were used that should mimic or exceed worst-case packaging scenarios with favorable results. “Contact ratios” herein refers to the cubic centimeters of sulfurous vapor per gram of the sulfur scavenger.
Zinc ionomer can be incorporated into films that include an oxygen scavenger. Zinc stearate is GRAS and has essentially no effect on the optical properties of polymer layers. Colored iron oxide powder and copper powder can be used in polyethylene or in conjunction with zinc ionomers to further increase the capacity. Copper powder or copper oxide of the appropriate particle size can be used at levels that have acceptable optical properties.